(revised abstract) Excitotoxicity plays a central role in the pathophysiology of epilepsy, stroke and head trauma. Overactivation of glutamate receptors leads to calcium overloading, triggering neuronal cell death. However, efforts to develop ionotropic glutamate receptor antagonists as neuroprotective agents have yet to be successful;alternative molecular targets for developing neuroprotective compounds need to be identified. Metabotropic glutamate receptors (mGluRs) are a family of G-protein coupled glutamate receptors. Group I mGluRs (mGluR1 and mGluR5) have been implicated in seizures and excitotoxicity. However, the underlying mechanism of excitotoxicity mediated by group I mGluRs is not known. The main hypothesis of this application is that group I mGluRs contribute to seizure and excitotoxicity by activating the canonical transient receptor potential (TRPC) channels, which is a subgroup of the TRP superfamily of non-selective cation channels. TRPC channels are identified as store-operated calcium channels (SOC) and are also activated by G-protein coupled receptors coupled to phospholipase C, such as group I mGluRs. Our preliminary data suggest that the TRPC1/4/5 subgroup of TRPCs, activated by group I mGluRs, play a critical role in the plateau potential underlying the epileptiform burst firing induced by group I mGluR agonists in the lateral septum, a limbic structure highly vulnerable to seizure-induced excitotoxicity. To follow up on this initial finding, Specific Aim 1 of this study will examine whether this plateau potential can be abolished by eliminating TRPC channels with TRPC channel blockers and by using a genetic knockout approach for specific TRPC channels. Specific Aim 1 will also determine whether there is a causal link between the mGluR-mediated plateau potential and acute excitotoxicity in the lateral septum. To determine whether TRPC channels contribute to seizure and excitotoxicity in vivo, the well-established pilocarpine- induced limbic seizure model will be used. Specific Aim 2 will test the hypothesis that TRPC1 and TRPC4 contribute to susceptibility to pilocarpine-induced seizures in vivo; and Specific Aim 3 will determine the distinct roles of TRPC1 and TRPC4 in neurodegeneration caused by pilocarpine-induced seizures in vivo. The long-term goal of this project is to elucidate the specific role of distinct TRPC family members in excitotoxicity. (description of abstract revision) The changes made to the abstract involve a deletion of all mention of experiments dealing with the use of the TRPC5(-/-) or TRPC1(-/-)/TRPC5(-/-) knockout mice. In addition, the signaling studies mentioned in the abstract have been deleted. All else has remained the same since the proposed experiments to remain in the grant address the original scope of the grant.